So copper conducts heat better but overall for a flashlight it’s worse? I’m having a hard time following XD
In addition to thermal conductivity issues, titanium has the clear disadvantage of undermining the tailcap lockout feature—an important one on this light.
If I’m not mistaken, there should be tailcap lockout. Current is interrupted at the tailcap PCB, and current does not travel via tailcap itself.
Do any of you guys realize what titanium and machining titanium costs? This is cheap for the size of the piece plus electronics, wages, and other costs.
As for appeal, why do people buy expensive cars, jewelry, sports memorabilia, etc…
You can gain a rudimentary understanding of how natural convection and radiation contribute to overall heat transfer by looking at the well-understood model for a horizontal cylinder suspended in a fluid. This doesn’t account for the addition of conduction into the hand and the lost surface area for convection, nor for any type of forced convection (e.g. wind) but it’s a reasonable starting point.
Here is a calculator that will determine the total heat transfer, split between natural convection and radiation, for such a case: Maya HTT - Thermal Wizard
I entered the approximate dimensions of the D4 in meters (.094 L x .024 D) and the approximate emissivity for anodized aluminum (0.8 - quite good!). At an ambient temperature of 20°C and cylinder surface temperature of 50°C (about as hot as you can hold continuously), the D4 can only get rid of about 2.5W. That’s 1.4W by convection and 1.1W by radiation.
At an emissivity of 0.2, which seems to be closer to the value for machined titanium, the total heat transfer drops to only 1.7W, with the same 1.4W from convection and only 0.3W from radiation.
It’s worth pointing out that these rates of heat transfer are at steady-state when the heat generation is equal to the heat dissipation and temperatures are constant throughout the system. It’s obvious that the D4, even with the good emissivity of anodized aluminum, just does not have the surface area to dissipate anywhere near the amount of heat it generates at full power. In theory, thermal regulation should settle on a power level that results in 2.5W of heat generation in the aluminum D4 and 1.4W in the titanium.
More practical questions like how long a light can run before stepping down require more complicated models that look at how temperatures change over time on their way to steady-state, and do factor in the thermal conductivity of the material (notice how that doesn’t matter in a steady-state analysis).
I just took a closer look and you appear to be correct - as long as the PCB’s copper layer does not contact the tailcap body. It comes pretty close to the edge.
I can’t check any of my aluminum tailcaps for continuity to the PCB because, well, they’re anodized.
So, as far as I can understand, buying titanium or copper flashlights is more a matter or durability and aesthetic than performance? Since copper will oxidize anyway, performance-wise it will end up being close to aluminium?
Not quite, copper will allow a much more heat to be absorbed before it gets as hot as an equal volume of aluminum. I’d compare it to high capacity vs low capacity batteries. Longer to charge at a given rate.
Is it more difficult than machining stainless steel?
Because they have money to spare…
I think the copper ‘engine’ is a good idea for the D4, but they should have chosen to rose gold plate it (to avoid the patina, keep it shiny) and stick with the Aluminium parts for heat management.
Copper and aluminum sounds good to me.
disagree
Copper is 69% MORE heat conductive than Aluminum.
see here
Titanium is 95% LESS heat conductive than Copper
Holding a flashlight in your hand moves MORE heat away from the body of the light, than freestanding the light in still air.
So when using a Titanium/Copper D4, the BEST way to keep it cool is to hold the Copper part in your hand. Holding the Titanium part won’t do much.
and btw, the reverse polarity protection of the D4 does not work. IF you put a battery in backwards it WILL heat up AND overdischarge (to prevent that, be sure to test turning on the light when you insert a battery)
video courtesy of RobertB
Conductivity is the travel of heat in the material itself and is not a bottleneck with CU and AL in flashlights, what interest us is the heat transfer coeficient through convection, it’s better with AL than CU, anodized AL is better than non anodized AL (17% advantage at 0 air speed, so only convection moves air), oxidized CU is better than non oxidized CU among other factors because the oxidized one has a larger surface area than polished one.
Edit: oh i see you edited your post.
I dont quite understand your post
are you agreeing that copper is more heat conductive than aluminum?
you seem to be focused on convection, if by that you mean heat transfer to AIR, that is not the primary cooling mode for a flashlight. Holding it in the Hand moves heat away by conduction, much more than still (no fan) air convection. Or maybe I misunderstand your terminology.
In any case, yes, the copper head will get a lot hotter than the Ti body.
There is heat transfer:
1) from led (primary heat source) to surface of flashlight ==> thermal conductivity of materials
2) Dissipation of heat from surface of flashlight to surrounding, whether it is air, or physical contact (hand). ==> radiation, convection and conduction.
I’m not a machinist but have been told that is a resounding YES.
For instance I once sent off a bunch of my Titanium items to be beadblasted my an industrial machinist whom I meet on CPF. It was the 1st time he worked with the material and -> upon blasting the Ti hot sparks/embers were sent all over his shop 
Apparently that’s one of Ti’s machining properties. Supposedly it machines quite differently than stainless steel. (But yeah, no first hand experience here. Perhaps the machinists on here can chime in.)
I agree the copper alloy called Brass is much lower conductivity than aluminum, but, I don’t think the D4 Ti is using a low conductivity alloy. If you have facts, please share, otherwise, your generalization may not apply. afaict, the copper head IS more conductive than Aluminum, since its Copper, not Brass
I didn’t quite see what you were arguing before you edited your post, now my answer seems off.
Seems reasonable to think that most of the heat transfer goes though the skin rather than the air granted one don’t wear gloves, but the useful surface area of exchange with the skin on the copper pill whatever way you hold the flashlight is teeny tiny compared to the one you would have holding the AL one with the full body being a vessel for heat, and the whole heat being concentrated on those fins would surely be quickly incomfortable to touch.
I’m still not sure what we are arguing, semantics, physics ?
I have a lot of copper lights, and they have not deformed. If you believe the D4 uses a low conductive alloy, please provide evidence
else, I am happy to assume it is pure copper, and NOT brass. (and I do agree brass is a copper alloy with. very low heat conductivity… almost as bad as Ti :-))
see https://intl-outdoor.com/emisar-d4ti-high-power-flashlight-p-927.html
_Features:
• Copper head (not brass)_
I was disagreeing when someone(s) suggested that aluminum moves more heat than copper (maybe I misunderstood, and the idea was meant to be that the aluminum D4 moves more heat than the Ti/Cu, which I do agree is possible).
I disagree that the copper used in the D4 has low conductivity
another perspective on the TiCuD4 heat management:
The Ti Body with the Copper Head is a major safety improvement. It allows the user to fire turbo without fear of burning their hand. Just hold the Ti Body, don’t touch the hot head, let the light do its thermal regulation thing. 
Since there is thermal regulation, the choice of metal is possibly less significant to the overall heat management of the D4.
On a side note, i was replying to your last message (#67) and went back to read one sentence and the whole answer was completely changed again, this is very confusing for the sake of the train of though going though the thread, i agree (i don’t see the safety point though) with your post #67 22:46 UTC time 7 of january 2018 version